# GPT-5.3 Codex

> OpenAI's agentic coding model with reasoning, tool calling and image input, listed by OpenAI as deprecated.

## Key facts

- Model author: OpenAI
- Input: $1.75 per 1M tokens
- Output: $14.00 per 1M tokens
- Cached input: $0.175 per 1M tokens
- Context window: 400,000 tokens
- Maximum output: 128,000 tokens
- Input modalities: image, text
- Output modalities: text
- Capabilities: reasoning, structured_output, tools, vision
- Released: 2026-02-24
- Knowledge cutoff: Aug 31, 2025
- Model IDs: `openai/gpt-5.3-codex`
- Model page: https://www.realrelay.ai/model/openai/gpt-5.3-codex

## Overview

GPT-5.3 Codex is a model from OpenAI built for agentic coding, where the model plans changes, calls tools and works across a codebase. It accepts text and image input and returns text, with reasoning, tool calling and structured output. OpenAI lists it as deprecated.

It has a 400K-token context window and can generate up to 128,000 output tokens. It accepts text and image input and returns text. Its knowledge cutoff is August 31, 2025, and it was released on February 24, 2026.

## Capabilities

GPT-5.3 Codex supports reasoning, tool calling, structured output and image input, and returns text output.

OpenAI documents GPT-5.3 Codex as an agentic coding model.

## Pricing

GPT-5.3 Codex costs $1.75 per 1M input tokens and $14.00 per 1M output tokens. Cached input reads cost $0.175 per 1M tokens. GPT-5.3 Codex is available through RealRelay's OpenAI-compatible API.

## Use cases

Use GPT-5.3 Codex for coding agents that read a repository, call tools to edit files and run tests, and report back; the 400K-token context window fits large projects.

Image input lets it work from screenshots of failing interfaces or architecture diagrams, and structured output lets build tools consume its results.

## Call it

OpenAI-compatible chat completions:

```bash
curl https://www.realrelay.ai/v1/chat/completions \
  -H "Authorization: Bearer $REALRELAY_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model": "openai/gpt-5.3-codex", "messages": [{"role": "user", "content": "Hello"}]}'
```

## FAQ

### What is GPT-5.3 Codex?

GPT-5.3 Codex is a model from OpenAI built for agentic coding, where the model plans changes, calls tools and works across a codebase.

### How much does GPT-5.3 Codex cost?

GPT-5.3 Codex costs $1.75 per 1M input tokens and $14.00 per 1M output tokens. Cached input reads cost $0.175 per 1M tokens.

### What is the context window of GPT-5.3 Codex?

GPT-5.3 Codex has a 400K-token context window and can generate up to 128,000 output tokens.

### What inputs and outputs does GPT-5.3 Codex support?

GPT-5.3 Codex accepts text and image input and returns text.

### Does GPT-5.3 Codex support tool calling?

Yes. GPT-5.3 Codex supports tool calling, along with reasoning, structured output and image input.

### When was GPT-5.3 Codex released?

GPT-5.3 Codex was released on February 24, 2026. Its knowledge cutoff is August 31, 2025.

### How do I call GPT-5.3 Codex via the API?

Call GPT-5.3 Codex through RealRelay's OpenAI-compatible API by setting the model name to openai/gpt-5.3-codex.